*In free space the velocity of electromagnetic waves is close
to 1 ft/ns; in limestone the velocity drops to about 0.3 ft/ns; and, in
coaxial cable, to 0.66 ft/ns. In the case of signals carried into the chambers
by the receiving coaxial cables, the observed velocity of propagation corresponds
to propagation down the outer shield of the coaxial cable, so that the
outer shield acts as a wire exciting a waveguide below cutoff. The same
phenomenon is frequently used to advantage in highway engineering--long
wires strung through highway tunnels fill the tunnels with local broadcast
transmissions, preventing loss of radio signals in automobiles traveling
in the tunnels. The passageways of the pyramids and/or most highway tunnels
are small enough at the radio wavelengths to act as waveguides below cutoff;
thus, radiation traveling down the passageway or tunnel is enormously attenuated
in very short distances, yet a long wire through such a tunnel can effectively
fill the tunnel with RF energy.